This application claims the benefit of Japanese Patent Application No. 2003-393516, filed Nov. 25, 2003.
1. Field of the Invention
The present invention relates to an apparatus for supplying a starting fuel to a fuel metering chamber of a carburetor before starting an engine.
2. Description of Related Art
A diaphragm-type carburetor may be employed as a fuel supply means of a general-purpose, internal combustion engine used as a power source of a portable working machine, such as a machine for use in agriculture, forestry, or the like. The supplying of fuel to an operating engine may be carried out as follows. The fuel is drawn from a fuel tank to a fuel pump by a negative pressure of a pulse pressure generated in a crank case or the like and is supplied to a fuel metering chamber by a positive pressure. The fuel then may be delivered to an intake passage via an idle port, a slow port, and a main nozzle, and is mixed with air to be supplied to the engine.
However, when there is little or no fuel in the fuel metering chamber when the engine starts, it may be desirable to supply fuel to the fuel metering chamber, so that the chamber may be filled prior to engine start, and it also may be desirable to supply extra fuel in order to improve the engine's low temperature starting properties at a cold start time. A starting pump may be provided for this purpose, and the engine may be smoothly started by manually operating the starting pump so as to supply fuel into the fuel metering chamber.
Such starting pumps include at least two kinds: a pressure-type structure (e.g., Japanese Unexamined Utility Model Publication No. 47-38218 and Japanese Unexamined Patent Publication No. 56-6049) and a suction-type structure (e.g., Japanese Unexamined Patent Publication No. 55-69748, Japanese Patent Publication No. 57-59417 and Japanese Unexamined Patent Publication No. 5-164001). The pressure-type structure may include a dome-shaped pump body portion generally formed from an elastic material, an inlet check valve placed in an inlet of a pump chamber in an inner portion of the pump body, and an outlet check valve placed in an outlet, and may have a fuel tank, a starting pump, a fuel pump, and a fuel metering chamber arranged in that order, for delivering fuel stored in the fuel pump to the fuel metering chamber via the starting pump. The suction-type structure may include a fuel tank, a fuel pump, a fuel metering chamber, and a starting pump arranged in that order for drawing air by the starting pump, for generating a negative pressure in the fuel metering chamber, and for feeding fuel from the fuel tank by the negative pressure. These structures may be properly selected depending upon the layout of the machine when the carburetor is mounted to the engine.
In the pressure-type starting pump described in the Japanese Unexamined Patent Publication No. 56-6049, the starting pump is placed in the middle of the fuel pipe passage which passage extends from the fuel tank to the fuel pump and is separated from the carburetor. In the suction-type starting pump described in Japanese Unexamined Patent Publication No. 55-69748, Japanese Patent Publication No. 57-59417 and Japanese Unexamined Patent Publication No. 5-164001, the suction passage which extends from the fuel metering chamber to an exterior portion of the carburetor, may be extended to place the starting pump in the suction passage in a location separate from the carburetor. In accordance with this structure, several alternatives exist for placing the starting pump in a readily operable location.
Nevertheless, when the suction-type starting pump is placed apart from the carburetor so as to be readily operable, a large space for storing air is formed within the suction passage between the fuel metering chamber and the inlet check valve installed in the starting pump. The air remaining within the suction passage during the engine operation flows into the fuel metering chamber and then is delivered to the intake passage from the fuel metering chamber together with the fuel, whereby a diluted air-fuel mixture is produced. Alternatively, the fuel may be delivered in a large quantity by a pumping effect caused by the residual air and an excessively dense, air-fuel mixture is produced, so that there is a risk that a malfunction of the engine may occur and a deterioration of exhaust gas may occur.